Many people wear protective safety helmets while enjoying outdoor riding activities such as snowmobiling, motorcycle riding and bicycling. Most helmets for snowmobiling and motorcycling, and some for bicycling, include a transparent or reflective face shield through which a rider can see. Unfortunately, moisture from the rider's breath tends to condense on the interior of the face shield and cloud the rider's vision. Face shield condensation is a particularly acute problem in cold weather because warm breath moisture rapidly fogs an ice-cold shield.
Various inventors have proposed schemes for reducing face shield condensation, but these schemes are impractical in very cold weather. Kamata discloses two such approaches in U.S. Pat. Nos. 5,058,212 and 5,093,938, which teach a helmet having an air vent on the helmet just below the face shield. Air flows into the vent and is then directed up along the interior of the face shield. The air ultimately follows a path through the interior of the helmet, finally exiting in the rear of the helmet.
In very cold weather, this flow of cold air through the interior of the helmet carries away substantial heat from the interior of the helmet. The rider becomes uncomfortable and, in the extreme climates often encountered on long snowmobile runs, may become dangerously cold. The rider may choose to shut off the air flow entirely to protect her body heat, but the face shield can quickly become nearly opaque from condensation.
Other proposals suffer from the same defects as Kamata. U.S. Pat. Nos. 5,170,510 (Nava), 4,704,746 (Nava) and 4,612,675 (Broersma) all disclose schemes that cause the defogging air to circulate at least partially throughout the helmet, thereby carrying away important body heat. Additionally, the Nava and Broersma systems cannot yield substantial defogging air flow along the interior of the face shield. Air can exit the helmets only through small exit vents, and there is minimal suction to pull air through the entry vents. This limited air flow can be a problem in very cold weather, where a substantial flow of defogging air is needed to be effective.